Coatings of thin dielectric films are useful in a variety of optical applications. For example, multi-layer dielectric thin-film coatings are often used to eliminate unwanted reflection (i.e., anti-reflective coatings) from surfaces in a variety of applications in the optical arts. Beam splitters and dichroic mirrors are useful in many optical applications, and may benefit from multi-layer dielectric stacks.
One well-known example of a multi-layer stack of dielectric thin-films is a quarter-wave stack. The quarter-wave stack is made up of a number of dielectric layers having an optical thickness corresponding to one-quarter wavelength of a particular chosen wavelength. Typically, the layers of dielectric material have alternating high and low indices of refraction. Light is usually incident normal to the surface of the quarter wavelength stack. However, angles of incidence other than the normal, up to approximately 30°, may be used with very little degradation in the response of the dielectric stack. In general, the effect of increasing the angle of incidence relative to the normal is a shift in the reflectance curve down to slightly shorter wavelengths.
Often, the layers of dielectric materials of a multi-layer dielectric stack optical filter have indices of refraction and thicknesses chosen to be transmissive of a desired wavelength. The desired wavelength of light will be transmitted, while all other wavelengths will be substantially reflected.
As the optical communication industry applies the dielectric thin-films stack in a variety of applications, there is an increasing demand for a technique to fabricate dielectric thin-films stacks en masse in a reliable manner.